1. Field of the Invention
The present invention relates to a rolling bearing apparatus with a supply unit that supplies a slight amount of lubricant to a bearing portion and a lubrication unit that supplies a slight amount of lubricant to rotating components such as a rolling bearing.
2. Description of Related Art
Rolling bearings are used as spindle bearings for machine tools. Some rolling bearings adopt oil-air lubrication in order to ensure appropriate lubrication of the rolling bearing (see, for example, Japanese Patent Application Publication No. 2009-58091 (JP 2009-58091 A)). However, the oil-air lubrication involves high running costs due to air consumption and needs incidental facilities such as an oil-air supply apparatus and an air clean unit, possibly leading to high facility costs.
As another means for lubricating a rolling bearing, a bearing apparatus incorporating a lubrication unit is known (see, for example, Japanese Patent Application Publication No. 2004-108388 (JP 2004-108388 A)). In the bearing apparatus, an annular lubrication unit is installed on a fixed bearing ring (fixed ring) of an inner ring and an outer ring, and the rolling bearing and the lubrication unit are integrated together. The lubrication unit includes a tank in which a lubricant is stored and a pump that discharges the lubricant in the tank into an annular space between the inner ring and the outer ring.
A slight amount of lubricant is discharged from the pump. The amount of lubricant discharged is adjusted by controlling operations of the pump. The lubricant is intermittently (at time intervals) discharged by the pump in the form of droplets. The amount of lubricant discharged from the pump during a single operation is, for example, several picoliters to several hundred nanoliters. In a bearing apparatus including such a lubrication unit as described above along with a rolling bearing, a slight amount of lubricant can be discharged into the annular space formed between the inner ring and the outer ring. The discharged lubricant adheres to raceway surfaces of the inner and outer rings and to rolling elements, thus allowing the rolling bearing to be lubricated.
In a bearing apparatus including such a lubrication unit as described above, for example, the outer ring is fixed to a bearing housing, and when the inner ring rotates integrally with the rotary shaft, rolling elements and a cage also rotate in the same direction. Thus, in a gas in an annular space between the inner ring and the outer ring, a vortex flow in the same direction as the rotating direction of the cage is generated. When a slight amount of lubricant as described above is discharged into the annular space where such a vortex flow occurs, the slight amount of lubricant may be affected by the vortex flow and precluded from reaching the raceway surface and the rolling elements. In other words, the arrival of the lubricant on the raceway surface may be hindered by the environment in the annular space, making the desired supply of the lubricant to the raceway surface difficult.